Method for producing ends of metal of composite pipe lengths

ABSTRACT

The invention relates to a method for producing ends of metal of composite pipes, comprising a casing pipe ( 1 ) of metal and a load carrying sheath ( 6, 7 ) of reinforced plastics, which sheath is produced in that the reinforcement is filled with polymer through injection under vacuum through injection pipes, said reinforcement comprises a first reinforcement layer ( 6 ) and a second reinforcement layer ( 7 ). To achieve the above-mentioned ends of metal the invention suggests that a sleeve ( 2 ) of the same thickness of material as the first reinforcement ( 6 ) is attached to the casing pipe ( 1 ) at both ends of said casing pipe, that the first reinforcement layer ( 6 ) is applied thereafter to the same thickness of material as the sleeves ( 2 ) over the whole length of the casing pipe, that a sheet metal strip ( 3 ) of preferably the same material as the casing pipe and with a greater width than the axial length of the sleeves is attached at the sleeves, respectively, and wound together with the second reinforcement layer ( 7 ) onto the sleeves as well as onto a part of the first reinforcement layer ( 6 ), the sheet metal strip having a step-like reduced thickness in the direction of its width to a depth corresponding to the thickness of material of the second reinforcement layer ( 7 ), so that said second reinforcement layer will be placed between the winding layers of the sheet metal strip, while the part of the sheet metal strips not being stepped will lie against each other, forming an end totally of metal at the pipe length, said pipe length being finished by injection in both reinforcement layers of a suitable resin.

The invention relates to a method for producing ends of metal ofcomposite pipe lengths, particularly such pipe lengths comprising acasing pipe of metal and a load-carrying sheath of reinforced plastics,which sheath is produced by applying reinforcement onto said casing pipeand filling said reinforcement with resin through injection under vacuumby pipes or cannulas, said reinforcement preferably comprising a firstreinforcement layer closest to the casing pipe for carrying peripheralloads and a second reinforcement layer on the outside of thefirst-mentioned reinforcement layer for carrying axial loads on thepipe.

There is today no known techniques for producing ends of metal of suchcomposite pipe lengths, which ends are intended to be joined at eachother by known and classified techniques to form a pipeline of greatlength. Said pipeline has to withstand large pressure and hightemperature. Such pipelines are intended for production andtransportation of i.e. natural gas and oil.

Therefore, the object of the invention is to suggest a method forproducing ends of metal of composite pipe lengths, which ends can bejoined together by known and classified techniques, for instance bywelding or a flange coupling.

This object is achieved according to the invention in that a sleeve ofpreferably the same metal as the casing pipe and with the same thicknessof material as the first reinforcement layer is attached to the casingpipe at both ends of said casing pipe, wherein at least one of saidsleeves are provided with axial through holes for injection pipes andvacuum connections, that the first reinforcement layer is appliedthereafter to the same thickness of material as the sleeves over thewhole length of the casing pipe between the sleeves and placingsuccessively at the same time said injection pipes in parallelrelationship to the longitudinal axis of the casing pipe, that a sheetmetal strip of preferably the same metal as said casing pipe and with agreater width than the axial length of the sleeves is attached to saidsleeves, respectively, and wound together with the second reinforcementlayer onto the sleeves as well as onto a part of the first reinforcementlayer, the sheet metal strip having a steplike reduced thickness in thedirection of its width to a depth corresponding to the thickness ofmaterial of the second reinforcement layer, so that said secondreinforcement layer will be placed between the winding layers of thesheet metal strip, while the part of the winding layers of the sheetmetal strip not being stepped will lie upon each other without anyintermediate reinforcement, forming an end surface totally of metal atthe pipe length, the pipe length then being finished by injection of asuitable polymer in both reinforcement layers.

A non-limiting example of the invention will now be described withreference to the accompanying drawings, in which

FIG. 1 is an end view of an end of metal of a composite pipe,

FIG. 2 is a longitudinal section of the end of metal attached to acomposite pipe, and

FIG. 3 is an enlarged longitudinal section of a metal strip with asteplike reduced thickness, in which step a part of the secondreinforcement layer is intended to be housed.

According to the invention, the casing pipe 1 of metal, preferablystainless steel, is provided at both ends with a sleeve 2 of the samematerial as the casing pipe, which sleeve is attached to the same bypressing and welding or brazing. The connection between sleeve andcasing pipe shall have a tensile strength larger than that of the pipe.Preferably, the sleeves 2 are attached flush to the ends of the casingpipe 1. At least one of the sleeves is provided with axial through holes(not shown). Through some of these holes suitable injection pipes orcannulas are to be inserted. The remaining holes are to be connected toa vacuum source (not shown) . A first reinforcement layer 6, preferablyin the form of a fabric, is then wound in multiple turns around thecasing pipe 1 between the sleeves 2, while at the same time placing theinjection pipes in said reinforcement. Preferably, the injection pipesare pulled through the holes in the sleeve so deep that the mouths ofthe injection pipes are located near the second sleeve and will lay inparallel relationship to the longitudinal axis of the pipe.

The first reinforcement 6 is wound to a predetermined thickness and thesleeves 2 have to have the same thickness of material, so that there isa smooth and plane transition section between the sleeves and thereinforcement. This first reinforcement is intended only to carry theperipheral loads on the pipe. A sheet metal strip 3, preferably of thesame material as the casing pipe, which strip has a steplike reducedthickness 4 along its width, is then attached to the sleeves,respectively, preferably by welding, in the longitudinal direction ofthe pipe and preferably flush to the ends of said sleeves. However, thesheet metal strip 3 has to have larger width than the axial length ofthe sleeves. This step 4 is large enough to house a second reinforcementlayer 7, which is used to carry only the axial forces on the pipe andwhich extends between the strips 3.

The sheet metal strip is then wound together with the secondreinforcement 7 in such a way that the non-reduced part 5 of the stripis wound onto the sleeve 2 and the second reinforcement will be placedbetween the different winding layers of the strip. When the secondreinforcement 7 has been wound to the end, the sheet metal strip isstill wound at least one turn, whereupon the edge of the strip isattached, preferably by welding, to the underlying winding layer. Thisresults in that the winding layers of second reinforcement 7 areenclosed between the winding layers of the strip, and each fibre in saidreinforcement will have an attachment surface which is large enough forproducing a shear strength larger than the tensile strength of thefibre.

During this winding operation of the strip 3 together with the secondreinforcement 7 onto the pipe the stepped part 4 of the strip and thepart of the second reinforcement 7 covered by the stepped part of thestrip is coated (wetted) either in that polymer is supplied in liquid orpowder form depending upon which type of polymer that provides theadhesive power. This means that if a thermosetting plastic is used thetotal gluing between the second reinforcement and the stepped part ofthe sheet metal strip will be completed, when the strip 3 and the secondreinforcement 7 have been wound to the end. If a thermoplastic is used,said thermoplastic is heated, after that the second reinforcement andthe sheet metal strip have been wound to the end, and melted and thenallowed to solidify for fastening the reinforcement between the surfacesof the strip. Also in this case the gluing is completed.

When the winding of the reinforcements 6, 7 and the sheet metal strip 3is finished, the pipe is placed in a suitable mould, not shown, which islifted essentially vertically and connected in its upper part to aninjection pump and a vacuum pump, not shown, whereupon the injection ofthe polymer is carried out in known manner.

In this way a composite pipe is obtained with ends of metal, theadhesion of which in axial direction is greater than the correspondingstrength of the total tensile strength of the laminate in axialdirection.

This means that it is possible to join composite pipe lengths of theabove mentioned type in any known manner and by classified techniques,i.e. by butt welding the ends, by flange couplings and so on.

It shall be mentioned that the part 4 of the sheet metal strips, whichhas a steplike reduced thickness, can be provided with holes or can beblasted for producing a rough surface to increase the adhesion powerbetween the polymer and the strip.

In another type of composite pipes, which is not produced by theabove-mentioned injection method, but comprises a casing pipe of metaland a load carrying sheath of reinforced plastics, which sheath isproduced preferably by prepregs and which over its entire cross sectionin radial direction carries at the same time both peripheral loads andaxial loads on the sheath, the above-mentioned sheet metal strip 3 isattached directly at the ends, respectively, of the casing pipe withoutthe intermediate sleeve 2.

What is claimed is:
 1. A method for producing ends of metal of compositepipe lengths comprising a casing pipe of metal and a load-carryingsheath of reinforced plastics, which sheath is produced by applyingreinforcement onto said casing pipe and filling said reinforcement withresin through injection under vacuum by pipes or cannulas, saidreinforcement comprising a first reinforcement layer closest to thecasing pipe for carrying peripheral loads and a second reinforcementlayer on the outside of the first reinforcement layer for carrying axialloads on the pipe, characterized in that a sleeve of the same metal asthe casing pipe and with a same thickness of material as the firstreinforcement layer is attached to the casing pipe at both ends of saidcasing pipe, wherein at least one of said sleeves are provided withaxial through holes for injection pipes and vacuum connections, that thefirst reinforcement layer is applied thereafter to a same thickness ofmaterial as the sleeves over the whole length of the casing pipe betweenthe sleeves and placing, successively simultaneously, injection pipes inparallel relationship to a longitudinal axis of the casing pipe, that asheet metal strip of the same metal as said casing pipe and with agreater width than the axial length of the sleeves is attached to saidsleeves, respectively, and wound together with the second reinforcementlayer onto the sleeves as well as onto a part of the first reinforcementlayer, the sheet metal strip having a steplike reduced thickness in adirection of its width to a depth corresponding to a thickness ofmaterial of the second reinforcement layer, so that said secondreinforcement layer will be placed between the winding layers of thesheet metal strip, while the part of the winding layers of the sheetmetal strip not being stepped will lie upon each other without anyintermediate reinforcement, forming an end surface totally of metal atthe pipe length, the pipe length then being finished by injection of asuitable polymer in both reinforcement layers.
 2. A method according toclaim 1, characterized in that a polymer in a form of a liquid or powderis applied simultaneously as the stepped sheet metal strip and thesecond reinforcement are wound onto the pipe length onto the surfaces ofthe stepped part and that part,of the second. reinforcement, which iscovered by said stepped part.
 3. A method according to claim 1,characterized in that the surface of the stepped part of the strip ismachined for achieving better adhesion.